The investigation centres on a graphic image of an ethnic man being tortured.

It is believed the detective sergeant is accused of introducing the email into the police computer system.

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The ethical standards department has been using computer experts to track the email.

One senior police source said the audit had shown that several police had added ''sickening'' racist comments before forwarding the email.

Chief Commissioner Simon Overland told The Age the audit had discovered ''a number of racist emails''.

He said police who introduced the material into the internal computer system would face dismissal.

Police who received the image but did not send it on would not be disciplined, those who forwarded it would be cautioned and those who added racist comments faced more serious internal charges. But sources said only the detective sergeant accused of initiating the email would face the sack.

Office of Police Integrity director Michael Strong last week revealed an inquiry into racism had been launched. It is believed he was referring to the email scandal.

Earlier this year Deputy Commissioner Sir Ken Jones issued a warning to all police that sending inappropriate emails could result in dismissal.

Mr Overland admitted last week there was a racist minority within the police force and vowed to move against them.

''The investigation into an offensive email that has been circulated internally is continuing and measures will be taken against anyone found to be involved,'' he said.

''It is unacceptable at any level. We will move decisively against anyone within our organisation who shows racial intolerance.''

He said he was bitterly disappointed at the email scandal. ''We are better than that and we don't need people with those attitudes in our system.''

Police Association secretary Greg Davies said police were concerned at the Chief Commissioner's power to sack on the grounds of no confidence.